The Ultimate Guide To Keeping Moorish Idol (Zanclus cornutus)
By: Kent Glover
A Professional Aquarist's Experience Keeping Moorish Idol For 2+ Years
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Summary
Summary
Moorish idol (Zanclus cornutus), or kihikihi in ʻōlelo Hawaiʻi, are among the most iconic reef fish in the world, yet they are rarely kept successfully in aquaria. These delicate fish often deteriorate during transport or succumb to parasitic infections once removed from their wild environment. Even if they accept food, their lifespan in captivity is typically short causing them to be considered "impossible" to keep successfully (Dodds, 2008).
I developed a methodology for successfully keeping wild-collected specimens, allowing aquarists with the necessary commitment to improve the survival rate of this species. My findings show that Moorish idol require an intensive quarantine protocol, including hydrogen peroxide baths, freshwater dips, and tank transfers. If conditions are stable and parasites are eliminated, feeding is relatively straightforward. Within a week of collection, they accept flakes, frozen foods, and nori. Once eating well, these fish prove to be hardy but remain highly susceptible to parasitic infections such as Ich, Marine Velvet, Flukes, and Worms. They tolerate medicated foods and baths well, but aquarists must be equipped with the knowledge and correct medications to treat quickly and effectively. Long-term health requires a varied, nutrient-rich diet provided multiple times per day, adequate tank conditions (100+ gallons) and extreme vigilance to prevent parasitic or bacterial infections.
Moorish idol eating from my hand after 2 years and 4 months from collection.
Species Profile
Species Profile
Zanclus cornutus (Linnaeus, 1758)
Class: Actinopterygii
Subclass: Neopterygii
Order: Acanthuriformes
Suborder: Acanthuroidei
Family: Zanclidae
Common name: Moorish idol
Hawaiian name: kihikihi
Description and Characteristics:
The Moorish idol is one of the most iconic and recognizable reef fishes in the world. With its unusual body features and striking coloration, the Moorish idol has been heavily portrayed in artwork and media around the world as a prominent coral reef inhabitant. Moorish idols are small reef fish that inhabit shallow flat reefs, turbid lagoons, and rocky and coral reefs. Their bodies are strongly compressed and disk-like with a tubular snout and small terminal mouth for scraping sponges and polyps off reef crevices. Their vertical white, yellow, and black bands contour their body, with a large white dorsal fin made up of VI-VII spines that includes an elongated, whip-like, III spine that extends above and behind the body called the philomantis extension (Schofield, 2021). Adults are normally seen singly or in small groups while juveniles are usually seen in small schools, both can occasionally form large schools. The Moorish idol is diurnal, feeding on sponges, polyps, and small crustaceans during the day and darkening their coloration while hiding within reef caves at night. Only reaching 23cm in length, the Moorish idol is able to maintain maneuverability within complex reef habitats throughout its lifespan (Allen et al., 2003; Galván-Magaña et al., 1996; Randall, 2005).
The Moorish idol is the only extant species of the Zanclidae family, most likely descending from the only other member of the Zanclid family, the extinct Eozanclus brevirostris, which lived during the late Ypresian epoch of the Eocene in what is now northern Italy (Carnevale, 2014; Sepkoski, 2002).
Some butterflyfish in the genus Heniochus are known as bannerfish or false Moorish idols. These bannerfish possess similar body shape and coloration to the Moorish idol, even though the two fish are not closely related. This could be due to mimicry or convergent evolution, most likely a combination of the two.
Zanclus cornutus belongs to the suborder Acanthurodei, which also includes surgeonfish. The name Acanthurodei is derived from the Greek words for thorn and tail, stemming from the spines found on the caudal peduncle of surgeonfish. The Zanclid family does not possess this feature, meaning it can be inferred that as they evolved the caudal spine was no longer beneficial.
Distribution and Abundance:
Moorish idols are found in wide ranges in the Indo-Pacific, Eastern Pacific, Japan, and the Hawaiian Islands (Allen et al., 2003; Galván-Magaña et al., 1996; Randall, 2005). This wide distribution is due to their unusually long pelagic larval period. Juveniles settle onto the reef at 7.5cm, much larger than most reef fish, meaning that larvae have ample time to be swept globally by the ocean currents (Burgess and Axelrod, 1973; Johnson & Washington, 1987; Myers 1999). The Moorish idol is a very common and abundant fish on reefs within their range with no known major threats, making them listed as Least Concern by the IUCN red list (IUCN, 2021).
Ecology:
The Moorish idol inhabits a wide range of subtropical (24ºC - 28ºC) coastal habitats from extremely shallow turbid lagoons to rocky and coral reefs reaching depths of 180m. They are commonly found in murky and clear waters of shallow reefs, hiding in cave systems at night or when threatened. The Moorish idol is a benthic omnivore, mainly feeding on sponges, tunicates, coral polyps, and other encrusting organisms (Allen et al., 2003; Galván-Magaña et al., 1996; Randall, 2005).
Reproduction and Life History:
Z. cornutus has no sexual dimorphism, making it nearly impossible to sex this species. However, these fish mate for life, most likely using chemical and behavioral cues to determine sex. Moorish idols are pelagic spawners, releasing thousands of gametes into the water column at night. This allows the fertilized eggs to be taken by and drift with the currents as the eggs grow into larvae. Zanclid larvae are known for their unusually long pelagic larval stage, becoming free-swimming juveniles at up to 10 cm, almost five times the average size of reef fish at settlement (Burgess and Axelrod, 1973; Johnson & Washington, 1987; Myers 1999). After settling on the reef the juveniles grow until sexual maturity when they will then find a lifelong mate. It is not known at what size Z. cornutus reaches sexual maturity, the average lifespan is also unknown, although specimens in captivity are known to live 2-4+ years.
Behavior:
Z. cornutus normally stay close to the reef, grazing on benthic and encrusting organisms throughout the day. Similar to the closely related surgeonfish, the Moorish idol uses its pectoral fins to swim exhibiting labriform swimming. These fish usually form small schools of 2-3 individuals but can occasionally form large aggregations and schools of over 100 fish. There is no known courtship behavior known for the Moorish idol, however, it is known that this species mate for life and aggregate spawning has been obsered in Palau.
Postflexion Moorish idol larvae, 9.5mm (Johnson & Washington, 1987).
16.0mm Zanclus cornutus larvae (Strasburg, 1962).
Wild Moorish idol with multiple philomantis extensions. Observed multiple times at Halona Blowhole, O‘ahu approximately 30 feet.
Intentions & Goals
Intentions & Goals
Ideally, the aquarium trade would rely solely on captive-bred fish, supplemented by sustainable wild collection. However, this is not yet reality. My work aims to:
Reduce mortality rates of wild-collected fish due to improper care and lack of knowledge.
Promote responsible husbandry practices until aquacultured specimens become widely available.
Contribute to the eventual captive breeding of Moorish idol, reducing reliance on wild collection and advancing sustainability in the aquarium industry.
For those who oppose any and all wild collection, I ask: How do we develop successful captive breeding techniques without first understanding the needs of wild fish? Responsible collection and careful study pave the way for a sustainable future in marine aquaculture.
Goals:
Develop a reliable quarantine protocol for Moorish idol.
Identify optimal feeding strategies for conditioning and long-term health.
Document behavior, growth, disease susceptibility, and other key factors.
Legal Considerations
Legal Considerations
It is completely legal to collect reef fish for personal use in Hawai‘i, provided all state regulations are followed. I strictly adhere to all local laws regarding aquarium fish collection.
Small scoop nets were used to collect all of my specimens, ensuring no harm to the reef including corals, rocks, or substrate.
Collection and Transportation Methods
Collection and Transportation Methods
I collected juvenile Moorish idol along shallow reefs near Ko‘olina, O‘ahu, on October 29, 2022. Using non-regulated fine mesh hand nets (~8-inch diameter), I safely captured a recently settled pair (~2.75 inches total length) without harming coral or reef structures. The fish were immediately placed in a 5-gallon seawater-filled bucket and transported to their quarantine tank within one hour.
Key transport considerations:
Dark containers reduce stress.
Even robust specimens experience significant transport stress.
Minimize transport time to improve survival odds.
For those purchasing from retailers in the USA, I recommend sourcing Moorish idol collected from Mexico or Hawai‘i, as they tend to be more resilient due to shorter transport times (Fenner, 2025). Ensure the fish is parasite-free, not emaciated, and ideally eating before purchase. If possible, transport the fish directly from the collection site to your tank as quickly as possible.
Here is a checklist derived from Fenner (2025):
Avoid newly arrived specimens — wait a few days before buying.
Don’t buy thin or emaciated fish — they rarely survive.
Skip damaged individuals, especially with frayed dorsal fins.
Look for bright coloration and active swimming during the day.
Choose fish that are alert, feeding, and not hiding.
Pair of Moorish immediately after collection being moved to a bucket for transport.
Juvenile Moorish idol in a freshwater dip before being moved to their quarantine tank. It is normal for fish to lay on their sides during freshwater dips, but move them immediately if they show significant signs of stress.
Showing lighter coloration immediately after freshwater dip.
Quarantine Protocol
Quarantine Protocol
Quarantine is the most critical phase in ensuring the survival of Moorish idol.
Arrival Procedure:
A 5-minute freshwater dip before introduction to the quarantine tank.
Lights remained off until the following morning to minimize stress.
Treatment Schedule:
Hydrogen peroxide baths (30 min @ 10 ppm) followed by a 5-minute freshwater dip, repeated 2-3 times per week for a month.
Tank siphoning/water changes occurred while the fish were in treatment.
Previously collected juveniles (n=4) quickly showed signs of Cryptocaryon (Ich) or Marine Velvet (Amyloodinium ocellatum) when not quarantined properly. These baths significantly reduced parasite loads but did not always fully eradicate them.
Ideally, fish should be transferred to a completely clean tank after each treatment.
If fins are tattered, avoid hydrogen peroxide and use only freshwater dips. Moorish idol heal quickly, and Melafix (API) accelerates fin recovery while preventing bacterial infections.
Praziquantel can also be used if the specimens show signs of flukes or worms. Established Moorish idol handle Prazi treatments just fine.
After one month of quarantine and two weeks without signs of infection, Moorish idol should be parasite-free and ready for their permanent display tank—assuming they have a strong appetite.
Quarantine Setup
Quarantine Setup
For this pair, I used a 75-gallon tank with a 30-gallon sump, equipped with:
Overflow unit
Powerheads
UV sterilizer (Fluval)
BioBalls (biological filtration)
Chiller (temperature stability)
Mechanical filter pads
While tank transfer methods are ideal, they were impractical in my case.
Water Parameters:
Temperature: 78-80°F
pH: Stable at 8.2
Ammonia: 0 ppm (critical for this species)
Nitrate: 0-100 ppm (no observed negative effects)
Daily water testing and frequent water changes using UV-filtered and mechanically filtered seawater from O‘ahu ensured optimal conditions.
IMG_0542.MOVMy Moorish pair on day 2, picking at algae and flake foods.
IMG_1273.MOVMoorish idol pair in quarantine chowing down on flakes.
Feeding
Feeding
Moorish idol have rapid metabolisms and quickly become voracious eaters once acclimated.
The larger individual accepted light green/brown flakes within a few days, while the smaller fish initially grazed on tank algae before eating floating nori after 5 days.
Color preference: Green or natural-colored foods were more appealing than red or orange flakes.
Within 5 days, both fish accepted flakes, frozen mysis, and nori, though flakes and nori remained their favorites.
Feeding Schedule (4-5 meals daily):
Morning: Flakes and/or pellets soaked in Vitachem (or similar vitamin mix)
Afternoon: Meaty foods (Piscine Energetics Mysis & LRS Reef Frenzy)
Autofeeder (4x daily): Various pellets, including:
New Life Spectrum AlgaeMAX
Otohime C1/C2 (larval transition feed)
Additional high-quality marine pellets
Nori offered most days
Feeding frequency is critical. Fish fed only once or twice daily remained thin and grew slower.
Interestingly, I have observed wild Moorish idol eating Cheetos, bread, leaves, and flowers, suggesting that they are opportunistic feeders. In captivity, ensuring a stress-free, pathogen-free environment is more important than food selection for getting them to eat.
Example daily feeding regimen to keep Moorish idol fed a varied and nutritious diet for long term health.
Growth
Growth
Moorish idol exhibit rapid growth during their juvenile stages. The individuals I collected nearly doubled in size within six months, with significant changes in body shape and fin structure.
Their bodies became longer and bulkier, with shorter dorsal appendages (philomantis extensions), which are more characteristic of adults.
At around four inches, the species' namesake horn-like structures (cornutus) began developing above their eyes.
Their mouths, designed for grazing on benthic invertebrates, became more pronounced and extended.
Moorish idol have an exceptionally long larval duration, reported to be up to 270 days. This means they settle as relatively large juveniles (~3 inches in length) compared to other reef species.
The rapid growth observed in captivity indicates that a high-protein, well-balanced diet and stable, stress-free environments play a key role in their development.
Social Structure & Spawning
Social Structure & Spawning
Moorish idol are often observed in pairs or small groups in the wild, but they do not always tolerate conspecifics in captivity. This contradicts advice given elsewhere on the internet (Fenner, 2025). While I do believe they should ideally be kept in pairs or groups, this species can become extremely aggressive to conspecifics.
Initially, my pair coexisted peacefully for eight months, but then aggression suddenly escalated. The larger individual began bullying the smaller fish, resulting in:
Tattered fins and damaged dorsal filaments.
Changes in feeding behavior, with the bullied fish eating less.
Physical injuries, which led to complications such as Pop Eye.
The sudden shift in social dynamics suggests that dominance hierarchies may form as the fish mature (Lorenz et al., 1998). This behavior is reminiscent of tangs, their closest genetic relatives, which also display aggression toward conspecifics in confined spaces.
Sex Determination and Breeding Potential
Sex Determination and Breeding Potential
Moorish idol do not exhibit clear sexual dimorphism, making it difficult to distinguish males from females visually. Based on my observations, I believe genital pore analysis, a method used in tangs, could be applied to determine sex in this species.
For successful captive breeding, further research is needed to:
Determine ideal group sizes for reducing aggression.
Identify environmental cues that trigger spawning.
Develop larval rearing techniques suited to their long pelagic phase.
Suicide Mission Spawning?:
In Palau, the Moorish idol has been observed spawning in aggregations away from the reef. The fish ascend from the reef to the open water during the day, allowing predators to follow them. Gray reefs sharks attack the ascending Moorish idol in a feeding frenzy, leaving very few to return to the reef safely. This behavior is odd as these fish normally spawn over the reef and not in open water. This rare occurrence shows that reef sharks could have more impact on reef fish spawning behavior than previously thought (Etpison & Colin, 2018).
Moorish idol behaviors documented in Lorenz et al. (1998).
Water Quality
Water Quality
Contrary to popular belief, pristine water quality is not the sole determinant of success when keeping Moorish idol.
Stability is Key:
My fish thrived despite a temporary drop in pH to 7.7 (due to a water source issue), as long as conditions were stable and gradually corrected.
Ammonia is the most critical water parameter, even low levels cause burns and severe stress in this species.
Nitrate levels between 40-100 ppm had no noticeable negative effects on my specimens.
Ideal Water Parameters:
Ideal Water Parameters:
Temperature: 78-80°F
pH: 8.2 (but stable values are more important than exact numbers)
Ammonia/Nitrite: 0 ppm
Nitrate: <100 ppm
Salinity: ~35ppt or specific gravity of 1.026
Maintaining stable conditions with high dissolved oxygen and low organic waste buildup is more critical than chasing "perfect" reef tank parameters.
Long Term Care
Long Term Care
Many sources claim that Moorish idol cannot survive more than a year in captivity, but I (and others) have disproven this.
Keys to Long-Term Success:
Frequent feeding (4-5 meals per day).
Nutritionally diverse diet with a mix of marine pellets, frozen foods, and nori.
Vitachem soaked meal at least once per day.
Pathogen control through strict quarantine protocols.
Avoiding aggression by carefully monitoring social interactions.
Adequate tank conditions, 100+ gallons at a minimum.
In cases where I could not manually feed my fish multiple times per day, an autofeeder with pellets kept them thriving for over a week while I was away.
Complications Along The Way
Complications Along The Way
Despite my experience, I encountered several avoidable mistakes and learning opportunities:
1. Using Unfiltered Seawater
Early on, I introduced wild pathogens into my tank by using unfiltered seawater.
The result? Ich, intestinal worms, and bacterial infections.
Solution: Treatments using freshwater dips, hydrogen peroxide, Praziquantel, Melafix, and implementing UV sterilization and rigorous re-quarantine procedures, ensuring all future fish remained pathogen-free.
2. Pop Eye and Gas Supersaturation
My smaller Moorish developed Pop Eye due to a pump malfunction, which caused supersaturation of dissolved gases.
In an effort to reduce pressure, I anesthetized the fish and used a sterile needle to release trapped gas.
While the swelling subsided, the eye never fully regained full function. The fish adapted and was eventually re-homed to a friend's large well-established tank.
These experiences highlight the importance of proactive care and correcting mistakes quickly to ensure the best possible outcomes.
Final Thoughts
Final Thoughts
Through my over two-year experience keeping Moorish idol, I have demonstrated that these fish can thrive in captivity with the right care. However, their long-term sustainability in the aquarium trade will ultimately depend on successful captive breeding efforts.
Key Takeaways:
Moorish Idol are not impossible to keep, but they demand dedicated, high-maintenance care.
Frequent feedings, disease prevention, and social management are crucial to success.
Captive breeding should be the industry's goal, reducing dependence on wild collection.
By documenting my findings and refining care techniques, I hope to contribute to a future where Moorish idol can be sustainably bred in captivity making them a viable and ethical addition to the aquarium trade.
References
References
Allen, G., Steene, R., Humann, P., & Deloach, N. (2003). Reef fish identification: Tropical Pacific. New World Publications & Odyssey Publications.
Burgess, W., & Axelrod, H. R. (1973). Pacific marine fishes: Book 1. T.F.H. Publications.
Carnevale, G., Bannikov, A., Marramà, G., Tyler, J., & Zorzin, R. (2014). The Pesciara–Monte Postale fossil Lagerstätte: 2. Fishes and other vertebrates. Rendiconti della Società Paleontologica Italiana, 4, 37–64.
Dodds, K. (2008, January). Still impossible after all these years: Keeping Moorish idols. TFH Magazine. https://www.tfhmagazine.com/articles/saltwater/still-impossible-after-all-these-years-keeping-moorish-idols
Etpison, M. T., & Colin, P. L. (2018). Blue water spawning by Moorish idols and orangespine surgeonfish in Palau: Is it a “suicide mission”? Aqua, 23(4–15), 121.
Fenner, B. (2025, April 30). Tips on helping the Moorish idol to survive in captivity. Chewy. https://www.chewy.com/education/fish/saltwater-fish/tips-on-helping-the-moorish-idol-to-survive-in-captivity
Galván-Magaña, F., Abitia-Cárdenas, L. A., Rodríguez-Romero, J., Pérez-España, H., & Chávez-Ramos, H. (1996). Systematic list of the fishes from Cerralvo Island, Baja California Sur, México. Ciencias Marinas, 22, 295–311.
IUCN. (2021). The IUCN Red List of Threatened Species (Version 2021-2). https://www.iucnredlist.org
Johnson, G. D., & Washington, B. B. (1987). Larvae of the Moorish idol, Zanclus cornutus, including a comparison with other larval acanthuroids. Bulletin of Marine Science, 40(3), 494–511.
Lorenz, K., Okawa, K., & Kotrschal, K. (1998). Non-anonymous, collective territoriality in a fish, the Moorish idol (Zanclus cornutus): Agonistic and appeasement behaviors. Evolution and Cognition, 4(2), 108–135. https://philpapers.org/archive/ARAONS.pdf
Myers, R. F. (1999). Micronesian reef fishes. Coral Graphics. https://scholar.google.com/scholar_lookup?title=Micronesian+reef+fishes&author=Myers%2C+Robert+F.&publication_year=1999
Randall, J. E. (2005). Reef and shore fishes of the South Pacific: New Caledonia to Tahiti and the Pitcairn Islands. University of Hawai‘i Press.
Schofield, P. J. (2021). Zanclus cornutus (Linnaeus, 1758). U.S. Geological Survey, Nonindigenous Aquatic Species Database. https://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=2303
Sepkoski, J. J. (2002). A compendium of fossil marine animal genera. Bulletins of American Paleontology, 363, 1–560.
Strasburg, D. W. (1962). Pelagic stages of Zanclus canescens from Hawaii. Copeia, 1962, 844–855.
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